Replacing pickups in my spector Euro 4

[Soul Power]

So I recently got a spector euro, and I'm in love with the neck and the electronics, but I'm looking for a thicker sound...
In particular I am trying to achieve a similar tone to Rocco Prestia's bass line on "Drop it in the slot"
Which pickup should I replace in order to achieve this sound, the P or the J?
What manufacturer?
Or would it be wiser to replace the preamp?

 

[FunkMetalBass]

Try replacing the preamp first. It comes with EMGs, which can have a very thick sound. It's almost unanimous agreement that the preamp is the definite weak link.

I'd throw in an Aguilar OBP-3 or EMG BQS. I think you'll be amazed by the difference.

 

[Soul Power]

Thank you, I'm glad you cleared it up for me. I'm by no means an electronics guy---
This is it, right?
http://bass-guitars.musiciansfriend...487608&src=3WFRWXX&ZYXSEM=0&CAWELAID=26040402
Will I need to get anything in addition to this? I'm going to bring it to a luthier.
It also has a switch...there is no place for a switch on my euro, but a luthier should be able to get it in there without hurting its finish, right?